1. Field of the Invention
The present invention relates to a display device having luminous elements arrayed as pixels, and more particularly to a display device in which luminous elements of different luminosity characteristics are used to display a color image.
2. Description of the Related Art
Flat-panel display devices represented by liquid crystal display devices are widely used as monitor displays for a personal computer, a portable information terminal or the like. Recently, display devices that employ luminous elements, such as organic EL (Electro Luminescent) elements arrayed as the pixels attract attention, and active research and development thereof have been carried out.
In the liquid crystal display device, light is transmitted through each pixel and a color filter or the like to display a color image. Thus, transmittance of the pixel is controlled according to the voltage applied thereto. This control differs from that for each luminous element represented by the organic EL element. Luminance of the luminous element is controlled according to the amount of current supplied thereto. Accordingly, each luminous element requires a drive element having a sufficient current driving ability, such as a polysilicon thin film transistor (TFT). Further, it is required that deviations in the characteristics of the drive elements are minimized to display a uniform image. To comply with the requirements, improvements in production and addition of a threshold voltage compensation circuit for each drive element have been suggested.
To obtain a uniform color image, it is further required that the current-luminance characteristics of luminous elements for emitting light, for example, in red (R), green (G) and blue (B) coincide with each other. However, it is difficult to attain coincidence between these characteristics of the luminous elements since the luminous elements of different colors are formed of different materials.
As a technique to solve the problem, it is conceivable that the signal line driving circuit has three reference gradation voltage generating circuits for the luminous colors. These circuits generate groups of reference gradation voltages, which are determined independently for the luminous colors, to compensate for the differences in the current-luminance characteristics. This technique is the same as providing different signal line driving circuits for the luminous colors.
Since this technique increases the size of the display device circuit, low power consumption is not achievable. Further, the display device becomes more expensive due to the increase in the number of circuit components.